1. Field of the Invention
The present invention is concerned with the cracking and removal of shells from edible nuts. More particularly, the present invention concerns a method and apparatus for removing shells from edible nuts by impacting the shells with a free travelling high speed billet.
2. Description of the Prior Art
It has been known to use mechanical means for the cracking and removing the shells from nuts. In order to recover undamaged kernels, the nuts are usually first conditioned by moisturizing so as to make the kernel more pliable. Rupture of the nut shell material occurs when deformation of the shell causes stresses exceeding the ultimate strength of the shell material. The prior art shell cracking devices operated on the principal of introducing a constant deformation to the shell at relatively low speeds. According to these devices, the shell is fractured by compressing the nuts from the ends thereof. The nuts are then subjected to a severe shelling operation in which the shell fractures created by the compression are enlarged for removing the shells from the kernels.
However, these prior art devices suffered from several shortcomings. First, the shellers were mechanically agressive machines that successfully separated the kernel and shell at the expense of considerable breakage of the kernel. Moreover, the shells broke into relatively large pieces that required severe shelling to separate adhering kernels. Due to the incomplete cracking and subsequent sheller damage, extensive equipment and labor inputs were required to separate the kernel pieces from similar size shell material. In contrast, an ideal cracking machine should break the shell into small pieces without damaging the kernel so that a gentle operation separates the kernel from the shell.
Second, the prior art nut crackers operating on the principal of fixed deformation did not cause a constant nut deformation, due to variations in nut length resulting from the common practice of sizing nuts by shell diameter, rather than length.
Third, deformations of the nuts sufficient to crack the shell damaged the nut kernel as well. In unstressed nuts, a certain small space exists between the shell and the nut kernel. However, before reaching its yield point, the shell typically undergoes deformations greater than the length of this space such that the interior of the shell contacts the nut kernel. Moreover, this deformation is typically so great that the kernel itself is deformed to an extent greater than the bioyield point thereof. Thus, by the use of constant deformation of the nut at relatively low speeds for cracking the shell, the kernel is also damaged before the cracking of the shell occurs. Commercial crackers, such as the "Meyer Automatic Edible Nut Cracker" have attempted to overcome this problem by providing adjustable stops to limit the maximum amount of deformation, however this has not proven to be entirely satisfactory.
It has also been known that impulsive forces applied to structures will cause rupture of the structures with relatively small overall deformation (Marin and Sauer; 1964; "Members Subjected To Impact Loads"; page 396; In Strength Of Materials, second edition, the MacMillan Co., New York). However, no prior attempt had been made to apply the principels of application of impulsive forces to the problems of cracking nut shells.